Poliomyelitis has existed for thousands of years, with depictions of the disease in ancient art. Poor sanitation, surprisingly, limited the spread of the disease as most people developed a resistance to the virus through constant exposure. But when sanitation was improved, beginning in the late 19th century in Europe and the United States, those areas began to experience major outbreaks of the disease, and the death rate began to increase. For more information, the Wikipedia entry is a good start. https://en.wikipedia.org/wiki/Poliomyelitis#History